Many types of communications can be performed over data networks (wireless and/or wireline networks), including electronic mail, web browsing, file downloads, electronic commerce transactions, voice or other forms of real time, interactive communications, and others. To enable the establishment of communications sessions in a network, various control functions are deployed in the network. Some standards bodies have defined subsystems within communications networks that include such control functions. One such standards body is the Third Generation Partnership Project (3GPP), which has defined an Internet Protocol (IP) multimedia subsystem (IMS) protocol that includes various control functions for provision of IP multimedia services, including audio, video, text, chat, or any combination of the foregoing.
An IP multimedia subsystem can be used in conjunction with wireless access networks, such as a wireless access network according to the GSM (Global System for Mobile) or UMTS (Universal Mobile Telecommunications System) standard, as defined by 3GPP, a wireless access network according to the CDMA 2000 (Code Division Multiple Access 2000) standard, as defined by 3GPP2; or other type of wireless access networks.
As a mobile station moves about one or more communications networks, handovers have to be performed as the mobile station moves between different coverage areas served by different base stations or even different access networks. Potentially, the mobile station can move between different types of packet-switched access networks, or between a packet-switched access network and a circuit-switched access network.
In the context of a multimedia communications session (in which both voice data and non-real time data can be communicated, for example), the mobile station can be transferred to a session in which different parts of the multimedia communications are provided over different types of access networks. For example, the transfer may result in voice data being communicated over a circuit-switched access network, while the non-real time data is communicated over a packet-switched access network. Conventional techniques of performing transfers of mobile stations in the above context may not be efficient under certain scenarios.